Measuring drum for screwmicrometers



Dec. 18, 1934. I E. SCHELLER I I 1, 8 61 MEASURING'DRUM FOR SCREW MICROMETERS Filed Jan 28, 195:5

In vehzf'on."

Patented Dec. 18, 1934 UNITED STATES PATENT orrica MEASURING DRUM FOR SCREW- MICROMETERS Ernst Scheller, Jena, Germany, assignor to firm Carl Zelss, Jena, Germany Application January 2a, 1933, Serial No. 854,045

. In Germany February 3, 1932 1 Claim.

I have filed an application in Germany, February 3, '1932.

The reading devices of screw micrometers, as

are used for instance with screw-micrometers 5 for general purposes, with eye-piece micrometers of optical instruments, and the like, generally have two scales which are provided, respectively, on the fixed part of the micrometer, so as to indicate complete rotations of the gauging l0 screw, and on the free end of the measuring drum, so as to permit reading the fractions of a complete rotation. The indices for these two scales are, respectively, the free edge of the measuring drum itself and a line on-the fixed part of the micrometer. Making the said free edge provide an index is not practical, because this edge is to have in this casea certain thickness in order to be protected from alterations due to use and wear. This increased thickness renders a reading more diflicult, and the measuring drum prevents the user of the instrument from seeing part of the scale. Although this construe-- tion is undesired in any case, ithas not been possible so far to replace it by another.

According to the invention, that part of the measuring drum which glides over. the scale indicating complete rotations is transparent and provided with an index for this scale, the drum edge being no longer required to bear an index.

30 The said drum part is given the requisite transparency by making it of glass, celluloid, or the like.

The scale for the reading of the fractions of' a complete rotation is conveniently provided on the transparent part of the drum, at a certain distance from the drum edge, and this in order to completely dispense with using'this edge. To avoid the possibility of a parallax between the (.Cl. 33-168) v scales and their indices, it is appropriate to provide the index and the scale of the measuring drum on the interior surface of this drum.

The accompanying drawing, which illustrates the invention, represents byway of example a 6 measuring drum used in connection with an eyepiece micrometer. v

In a bearing a is disposed a gauging screw b.

On this bearing a, which represents the fixed part of the micrometer and is connected to an 10 ocular c, is rotatably disposeda drum d fixed to the screw 1). The cylindrical part d! of this drum d is of glass. The surface of the fixed part, that is to say of the bearing a, is provided with a scale e and an index I. The glass cyl- '1 inder d the free edge of which is designated d, has on'its interior surface a scale I and an in- .dex e Complete rotations of the drum d are indicated on the scale 0 by the index e and the fractions of a complete rotation on the scale I 2 by'the index I.

It follows from the above that the edge d of the drum d is no longer required for the reading and need therefore not bear any scale.

I claim:

. 25 A measuring drum for screw micrometers, having at its front part an index for indicating 

